In recent years, development of technology for wirelessly transmitting power (electric energy) without using power cords has been popular. Among the methods of wirelessly transmitting power, a so-called magnetic resonance method is the technology that has been attracting particular attention. The magnetic resonance method was proposed by a research group at the Massachusetts Institute of Technology in 2007. The relevant technique has been disclosed in Patent Document 1 (Jpn. PCT National Publication No. 2009-501510), for example.
In a wireless power transmission system of the magnetic resonance method, the resonance frequency of a power transmission-side antenna is equal to the resonance frequency of a power reception-side antenna; the antennas of a high Q-value (100 or more) are used. Accordingly, the energy is transmitted from the power transmission-side antenna to the power reception-side antenna in an efficient manner. One of the major features is the power transmission distance that can be set to between several tens of centimeters and several meters.
As for the above wireless power transmission system of the magnetic resonance method, a study has been going on to apply the wireless power transmission system to charging vehicle-mounted batteries such as those of electric vehicles (EV) and hybrid electric vehicles (HEV). If such a wireless system can be used for the above vehicles, it is possible to eliminate the need to handle power connectors or power lines when power is to be supplied to the vehicles.
For example, Patent Document 2 (JP2010-68657A) discloses one antenna that is mounted in a bottom surface portion of a moving body such as an electric vehicle; power is wirelessly transmitted from another antenna that is installed on the ground, and the transmitted power is used to charge a battery of the electric vehicle.
[Patent Document 1]
Jpn. PCT National Publication No. 2009-501510
[Patent Document 2]
JP2010-68657A